Rosemary Ainslie COP>17 Circuit / A First Application on a Hot Water Cylinder

[Rosemary Ainslie]

To be correct - I would estimate these figures for current pulses >5ms.
In your circuit you have pulsed DC with  500us pulse duration.

I don´t know your batteries - nor do I have my own data or data from a battery manufactorer at hand so - nothing we can base on.

If we reach down to 1us - I would estimate the internal resistance in the area of few ohms. For 500us - a current from 2-5Amps would sound reasonable.

This is why I heavily suggest to determine the AC input/output resistance of batteries used with such setup.

How to determine AC impedance of a battery ?
Use 80´ties DC coupled HIFI-AMP+sinus generator+output capacitor.
(or industrial servo amp or similar)
Determine the internal resistance as function of frequency using low inductive precise test load (1Ohm).
Measure damping as function of frequency if feeding to battery terminal.
The battery impedance can then be calculated from that damping function corrected with the values from the 1Ohm test.

rgds.

fritz

Fritz  - thanks for this.  It actually gives me a little renewed hope.  If the current can be restricted to 2 amps we're still in business.  I get it we just need to look to the timing of the switch.  I'll look to doing that battery impedance test.  We're getting delivery of our first bank - acid - in the near future.  I'll photograph them when they're to hand.

[fritz]

(ASIDE - all this makes me wonder: why did the previous replicators use such 'heavy-duty' scopes and collect so much electrical data, if the excess output energy is thermal rather than conventional volts & amps?)

"heavy-duty" scopes have the formfactor of a microwave, a DVD burner 1Gb of memory and a 15inch display.
Saw one today. Is used to analyze the IF of our WLAN tranceiver. But too big to steal.

[fritz]

If the current can be restricted to 2 amps we're still in business. 

A similar setup as used with stepper motor chopper could be useful.
For high performance stepper motor applications - you use for example stepper motors rated for 3Volts with 24Volt excitation.
With i=L*du/dt you can get fast more current into that ugly coil using 24Volts.
To protect the 3Volt motors from burning down - you have a shunt resistor for sensing the current. If the current exceeds whats rated - its turned  off using slow or fast decay.


For you circuit this could mean - turn the mosfet on by timer - and turn it off if target current is reached using flipflop to drive the motor - set on timer - reset if shunt voltage comparator reaches nominal amps ....

rgds.

[Rosemary Ainslie]

A similar setup as used with stepper motor chopper could be useful.
For high performance stepper motor applications - you use for example stepper motors rated for 3Volts with 24Volt excitation.
With i=L*du/dt you can get fast more current into that ugly coil using 24Volts.
To protect the 3Volt motors from burning down - you have a shunt resistor for sensing the current. If the current exceeds whats rated - its turned  off using slow or fast decay.


For you circuit this could mean - turn the mosfet on by timer - and turn it off if target current is reached using flipflop to drive the motor - set on timer - reset if shunt voltage comparator reaches nominal amps ....

rgds.

Golly Fritz.  I think we need to enlist you on the team.  I'll run your suggestions through with them.  I'm afraid my knowledge of these motors is zero.  But the others will know how to apply all this.  Thanks again.  I LOVE OPEN SOURCE.   

Kindest regards,
Rosemary

[fritz]

(...) using acid density/concentration meter meter as found in automotive shops with -non-service-free lead acid batteries - would be another option to get more grip on the "smiling buddha".